These materials often tend to undergo compaction creating solid lumps which hinder or even prevent material outflow.
These solid lumps are generally disintegrated and their constituent materials liquefied using powerful jets of air or other gases using a technique known as “firing”.
This technique almost instantaneously introduces a large quantity of compressed gas at high pressures into the vicinity of these solid lumps, to produce impact waves which disintegrate them.
The gas quantity introduced must be such as to completely disperse its kinetic energy into the material to be found in the silo or hopper.
In firing valves, in most cases, only the high pressure part of the outflow is important for the purpose to be attained. The low pressure tail represents only a fluid loss which must be re-established.
The useful energy of the air used in firing from the vessel regards the initial impact wave pulse at maximum pressure, between 5 and 10 bars (1 bar=100000 Pa), even better at a pressure between 7 and 10 bars, whereas the firing tail, below 7 bars, may not have any practical effect and represents a loss, considering that this tail is also reloaded into the vessel to restore the starting conditions.
In patent application MI2002A000627, a system of valves is described which enables air discharge to be limited upon reaching a pressure set by a pressure setting device. The valve system is composed of valves having a metal or, in any case, a rigid piston as the shutter.
In the patent application WO2008009337, membrane type shutters are used instead.